1. Field of the Invention
The invention relates to a microfluidic chip, which is utilized in a poly-enzyme chain reaction and hybrid array of biochemical experiments, and in particular to a microfluidic chip, which can be utilized to raise the efficiency of biochemical reactions.
2. Related Art
The poly-enzyme chain reaction is presently the most frequently used method for nucleotide multiplication and augmentation. The quantity of DNA (deoxyribonucleic acid) can be multiplied exponentially several million times through the repeated denatured, annealing and extension processes of the segments of DNA, by thermal circulation, so that the traditional time consuming process of bio-medical sample body treatment and its reaction schedule can be shortened significantly.
In the poly-enzyme chain reaction, the sample body must be augmented through a micro channel-electrode-on-chip device having electrodes and micro-channel disposed thereon, to speed up and facilitate the subsequent tests and examinations. To achieve this purpose, the microfluidic chip must fulfill the following requirements:
(1) it must be stably bonded and heat resistant against high temperature;
(2) it must be transparent to light to enable the observation by an optical system; and
(3) it must be conveniently connected to the subsequent bio-chemical reactions.
In general, the microfluidic chip is made of a chip bonding the micro-channel, and an electrode layer made of metal, and the bonding method utilized usually can be classified into the following three categories:                1. The anodic bonding: etching a microstructure on a silicon substrate: next, bonding the anode to a glass substrate having electrodes; then, bonding the two substrates together through high voltage and high temperature (approximately, 1000V and 400° C. respectively). The bonded glass substrate and silicon substrate thus produced has the characteristics of single side transmittance of light, however, the equipment required to use in this process is quite expensive, thus raising the production cost.        2. The chemical bonding; selecting the adhesive material suitable for use as a substrate interface; bonding the two substrates together through bonding the chemical bonds on the surface of the substrates. In this bonding method, different adhesive material is selected for bonding the substrates of different materials. However, the quality of the chip thus produced is not quite satisfactory, since the adhesive material is liable to block the micro-channel in the substrate. Besides, the bonding strength at high temperature is not sufficient enough.        3. The thermal fusion bonding: bonding two substrates together by heating the two substrates to the point of getting soft. The advantage of this method is that good bonding strength can be achieved between the two substrates, and the optical characteristics of the substrates are not affected after the bonding. However, it suffers from the drawbacks that quite a few materials are not suitable for use in the high temperature environment as required by this method.        
As to the classification of the microfluidic chip, it can be classified as fixed type heating and movable type heating depending on the manner of heating the test fluid. The main feature of the fixed type heating is that the test fluid is stationary and does not flow during the cooling or heating process. The temperature variations are controlled by the feedback of the temperature sensor to regulate the electric power used for heating, while in the moving type heating, the test fluid is made to flow to the various positions of the chip to achieve heating or cooling, and the heater is used to provide heat to achieve a fixed temperature at the various positions of the chip, and the temperature variations of the chip are obtained and controlled by driving the test fluid to the various positions of the chip by the outside force. In addition to the above-mentioned fixed type heating and moving type heating method, there is another non-contact type heating method, wherein the rise and fall of the temperature is achieved and controlled by heating the test fluid with the infrared light radiation and detecting the temperature variation by the sensor.
Besides, the microchannel-electrode-on-chip structure may be further classified as a single-faced type and a double-faced type depending on the disposition position of the electrode. The electrode is provided with a heater wire and a sensor wire. Ideally, the heater wire and the sensor wire are arranged as close to the test fluid in the microchannel as possible, as such to obtain the optimum heat conduction efficiency and actual temperature variations. However, in practice, due to restrictions of the manufacturing process and the temperature controlled environment, if the test fluid is allowed to directly contact the electrode, it is liable to cause the hydrolysis of the electrode, and its temperature control effect is not so good. To avoid the electrode being directly exposed to the test fluid, in the prior art, the method adopted is through utilizing the insulation layer and arranging the wirings of the electrode on the backside of the insulation layer or arranging the electrode in different layers. However, by doing so, the production cost will be raised significantly. In addition, the distance between the heater wire and the sensor wire will affect the temperature variation of the test fluid. If the sensor wire is arranged too close to the heater wire, then the temperature sensed by the sensor wire is the temperature variation of the heat source but not the temperature variation of the test fluid. On the contrary, if the sensor wire is arranged too far away from the heater wire, then the loss of heat energy is raised and the sensitivity of the temperature measurement is decreased. The details of the above-mentioned effects will be discussed more thoroughly as follows, in conjunction with the related drawings.
Refer to FIGS. 1A & 1B for the schematic diagrams illustrating the cross sections of two kinds of the microfluidic chips used in the prior art. As shown in FIG. 1A, the first arrangement utilized is to arrange the heater wire 10 and the sensor wire 12 on the backside of the microchannel 14 so that the heat conduction is done through the substrate 16. As such, the efficiency of heat conduction is reduced enormously, thus it is not easy to effectively heat the test fluid contained in the microchannel and measure its temperature accurately. Alternatively, as shown in FIG. 1B, in the second arrangement, the heater wire 20 and the sensor wire 22 are placed on the opposite side of the microchannels, so that the sensor wire 22 is closer to the microchannel, to be able to measure the temperature of the test fluid contained therein more accurately. However, in this arrangement, the additional insulation layer 26 utilized could incur additional production cost.